1. Field of the Invention
This invention relates generally to wireline-conveyable wellbore tools, and specifically to a wellbore tool string which includes a wireline-conveyable source of pressurized fluid and a fluid-pressure actuable wellbore tool.
2. Description of the Prior Art
Fluid-actuated wellbore tools are widely known and used in oil and gas operations, in all phases of drilling, completion, and production. For example, in well completions and work-overs a variety of fluid-actuated packing devices are used, including inflatable packers and bridge plugs. In a work-over operation, a fluid actuated wellbore tool may be lowered into a desired location within the oil and gas well, downward through the internal bore of wellbore tubular strings such as tubing and casing strings.
Recent advances in the technology have allowed fluid-actuated wellbore tools to be lowered into the wellbore through the production tubing on either a wireline assembly or a coiled-tubing workstring. Coiled-tubing workstrings are usually coupled to a pumping unit disposed at the surface, which provides pressure to an actuating fluid which is usually, but not necessarily, a wellbore fluid. The pump at the surface of the wellbore usually has sufficiently high levels of pressure to completely, and reliably, actuate the fluid-actuated wellbore tool. In contrast, wireline-suspended pumps which are lowered into the wellbore are subject to stringent geometric constraints, particularly when intended for through-tubing operations, and are thus low-power devices, which are rather delicate in comparison with conventional pumps.
A number of fluid-actuable wellbore tools may be used with wireline-suspended pumps. For example, fluid-actuated inflatable packing devices, such as inflatable packers and bridge plugs, which include substantial elastomeric components, such as annular elastomeric sleeves, can be run into a wellbore in a deflated condition and be urged by pressurized wellbore fluids between the deflated running position and an inflated setting position. In the inflated setting position, the elastomeric components of wellbore packers and bridge plugs are essential in maintaining the wellbore tool in gripping engagement with wellbore surfaces.
It is frequently necessary or desirable to pressure test portions of wellbore tools, well head assemblies, or portions of the wellbore, with high but transient pressure levels. This is especially true in the use of wireline-conveyable wellbore tool strings, which are typically lowered into a wellbore through a lubricator apparatus which is coupled to the uppermost portion of a wellhead or blowout preventer. Before running the wireline-conveyed wellbore tool into the wellbore, it is desirable to perform a high pressure test of the lubricator by closing off a well head valve and pressurizing the lubricator up to ten thousand pounds per square inch of pressure with a gas. This pressure test of the wireline lubricator is typically performed with the entire wellbore tool string disposed within the lubricator. Therefore, high pressure gas may be urged into interior regions of the wellbore tool string, in communication with a pressure-actuable wellbore tool, such as an inflatable packer or bridge plug.
When the pressure test of lubricator is discontinued, pressure is bled off from the lubricator. However, gas which is disposed or trapped within portions of the wellbore tool string may expand, causing an unintentional and problematic actuation of the fluid-actuable wellbore tool. Typically, fluid-actuable wellbore tools are difficult or impossible to move from a radially-enlarged set position to a radially-reduced running position. Therefore, inadvertent setting of a fluid-actuated wellbore tool while it is disposed within the lubricator assembly will require that the lubricator assembly be dismantled or destroyed in order to remove the wellbore tool from within it. This is an extremely undesirable result, since it impedes the workover operation, results in damage to, or destruction of, the lubricator, and may require that replacement fluid actuated wellbore tools and lubricator assemblies be procured before the job can be continued.